Soluble and membrane proteins of the secretory pathway enter the ER where they fold, are modified by carbohydrate addition and disulfide bond formation and assemble into complexes. Before exiting the ER, proteins must pass a quality control (ERQC) test. ERQC encompasses all those processes that ensure that only correctly folded/modified/assembled proteins exit the ER and includes retention in the ER, retrieval from downstream organelles and ER-associated degradation. ERQC contributes to the manifestation of disease either by depleting cells of essential proteins or by the toxic accumulation/aggregation of aberrant proteins. A progressive decline of ERQC in ageing highly differentiated neurons may play a major role in the neurodegenerative diseases such as Parkinson, Alzheimer's, Huntington's and prion diseases, all of which involve protein aggregation as the underlying pathology. The overall goal of this research is to understand the process of ERQC by defining the molecular components involved and determining how ERQC components function to recognize, retain, and retro-translocate misfolded substrates to be ubquitinated and degraded by the proteasome. The proposed project has four specific aims directed toward this goal. (1) The components of ERQC will be identified through a characterization of previously isolated ERQC mutants obtained at the end of the last grant period and through a genome wide mutant screen, synthetic genetic array analysis, synthetic lethal screen and micro array analysis to identify new components. (2) The role of ER to Golgi trafficking in ERQC will be examined through the use of retrograde trafficking mutants, cross-linking to Erv29p (a cargo receptor for ER exit) and determining the impact that glycosylation in the Golgi has on the degradation of ERQC substrates. (3) The aggregation of misfolded ERQC substrates in the ER results in their accumulation and associated cytotoxic effects. This specific aim is designed to identify ERQC substrate proteins that misfold and aggregate in the ER for use as a disease model in examining how cells contend with these potentially lethal accumulations. (4) A model substrate will assist in determining how soluble and polytopic membrane protein is treated differently by the ERQC. Knowledge and insights gained from these aims will lead to an understanding of the process of ERQC to be used to interpret protein aggregation based diseases.